The present invention has to do, in part, with a slip shaft having either an automatic or a conveniently adjustable mechanism for preventing axial migration of web spool cores. In a web converting facility it is frequently necessary to divide or slit a parent roll of web material into a series of smaller rolls of various widths. To do this the parent roll is unwound through a slitter machine and then rewound onto a set of web spool cores to form a set of uptake rolls, all of which are mounted on uptake shafts. The uptake rolls may have varying diameters because of treatment of the web material that takes place in the same operation as the slitting, increasing the web thickness. The varying uptake roll diameters create a need for different uptake roll rotational speeds in order for the web material linear speed to be the same for the web material traveling to each uptake roll. A slip shaft is typically used to accommodate this requirement when two or more uptake rolls are mounted on the same shaft. This is a shaft that permits the uptake web spool cores to slip (i.e. rotate a different speed) relative to the shaft. Various mechanisms may be used to maintain a steady web tension, but these are not part of the subject matter of this patent.
Unfortunately, cores that slip rotationally relative to a shaft, also have a tendency to slip axially along the shaft. A number of strategies have evolved to address the problem of axial migration of web spool cores on a slip shaft.
A first existing method for stopping the axial migration of cores is to equip the slip shaft with an axially aligned set of closely spaced core stops that are all urged outwardly by a long bladder that is pressurized after the cores have been placed on the shaft. Where a web spool core is present, the core stops are restrained from outward movement and provide pressure to the core interior to maintain the web in tension. Where the cores are not present, the core stops protrude, theoretically restraining the cores from axial migration.
A problem with this first existing method is caused by the fact that a first core stop that is restrained by a core will, in turn, restrain the bladder. Therefore, a neighboring second core stop will not be pushed outwardly very far, because the bladder is restrained by the first core stop in its vicinity. As a result, the desired sharp restraining border at each axial end of each web spool core is not formed and cores do, in fact, migrate.
A second existing method for stopping the axial migration of cores is to equip the slip shaft with a set of restraining core stops that are set into a bracket, an axial channel having a pneumatic bladder for pushing the bracket and core stops outwardly and temporarily fixed in place by set screws. This method is taught by Marin in U.S. Pat. Nos. 5,597,134 and 5,746,386. Although this stops the axial slipping, the requirement of manually unfastening the set screws, adjusting the core stops and then refastening the set screws is onerous, especially when, as is typical, the shaft is in a difficult to access location or requires an adjustment after the spooling process has started.
An additional method for stopping axial migration is by placing empty cores in between the roll cores. This method is a little difficult to adjust, and causes a good deal of rubbing at the edges of the cores, which is generally detrimental to the process.
Yet another known method for stopping the axial migration of cores is to equip a core shaft with two channels, each of which houses a pneumatic bladder and a set of core stops positioned radially outwardly of the bladder. When the bladder is inflated the core stops are held in position, preventing axial migration. When the bladder is deflated the core stops may be moved to new positions, to accommodate a different arrangement of cores. Unfortunately, this system has the weakness that the bladder must be deflated to permit a particular set of web spool cores to be removed. When the bladder is in this deflated state, there is nothing to prevent the core stops from moving, especially if contacted by the cores that are being removed, as is typically the case. Afterwards, even if the exact same previous arrangement of core stops is desired, the core stops must be repositioned to the positions that they had prior to the bladder deflation. In paper mills and other operations using slip shafts, it is typical to retain a set of core positions for at least a few of operations with successive sets of cores. In fact, sometimes the same core stop positions may maintained for weeks or months. With the method described in this paragraph, the mill personnel must repetitively perform the task of resetting the core stops, which would be unnecessary if there was some way to retain the core stop positioning between sets of cores.
Another problem encountered in the use of core stops is the tendency of web spool cores to "ride up" onto core stops, press downwardly upon them and flatten and "rode over" the core stops. When this happens, the core stops are unable to prevent the axial migration of web spool cores. With the stop inside the core, unwanted friction is placed on the core interior disrupting the slipping process.
Web core retaining shaft assemblies in general typically have tension segments that are pressed outwardly by an air bladder to maintain tension on the interior surfaces of the cores. Sometimes these segments protrude slightly even when the air bladder is not inflated, because, for example, a first segment could ride up and/or "catch" on neighboring second and/or third segments. When this happens, it may become quite difficult to remove one or more of the web spool cores from the shaft. If the web spool cores are removed automatically, the automatic removal mechanism could damage the cores and itself. In grip shafts another tension segment problem is encountered in the use of tension segments in helical air bladder accommodating channels such as those described in U.S. Pat. No. 5,445,342. Because existing tension segment designs cannot fit into these helical channels unless the tension segments are slightly pliable, elastomeric tension segments are currently used for this application. Unfortunately, elastomeric materials wear away faster than does steel. It would be beneficial if there was some way of using steel tension segments in a helical channel.